This invention relates to admixtures for use in extrudable hydraulic compositions, and extrudable hydraulic compositions which are uniform after mixing the components with a large amount of water.
In prior art hydraulic compositions adapted to be extruded into siding members or the like, lightweight aggregates such as perlite are used to improve applicability and reduce the weight. The use of lightweight aggregates, however, requires to increase the amount of water to produce an appropriate mixed composition, which in turn, sometimes causes the water-soluble cellulose ether serving as extrusion aids to form clumps in the mixed composition. Then all the amount of cellulose ether added is not effectively utilized. Also, it is sometimes attempted to condition pulp fibers to a water content of several tens of percents prior to use, in order to enhance the dispersion of pulp fibers. When such conditioned pulp fibers are used, the water content therein causes the water-soluble cellulose ether as the admixture to form clumps in the extrudable hydraulic composition. Then all the amount of cellulose ether added is not effectively utilized. In either case, cellulose ether must be added in excess of the necessity.
An object of the present invention is to provide an admixture for use in extrudable hydraulic compositions, which is well dispersible and utilized to its entirety in hydraulic compositions even in the presence of a large amount of water; and an extrudable hydraulic composition comprising the admixture.
The inventor has found that a nonionic water-soluble cellulose ether having an average particle size of at least 120 xcexcm is well dispersible in hydraulic compositions even in the presence of a large amount of water so that the entire amount of the cellulose ether added is utilized to exert its function.
Accordingly, the invention provides an admixture for extrudable hydraulic compositions, comprising a nonionic water-soluble cellulose ether having an average particle size of at least 120 xcexcm; and an extrudable hydraulic composition comprising the admixture.
The admixture of the invention for extrudable hydraulic compositions is defined as comprising a nonionic water-soluble cellulose ether having an average particle size of at least 120 xcexcm. The average particle size of nonionic water-soluble cellulose ether should be at least 120 xcexcm, preferably at least 150 xcexcm, and more preferably at least 180 xcexcm. With an average particle size of less than 120 xcexcm, nonionic water-soluble cellulose ether becomes fast dissolvable so that clumps are formed to reduce the amount of nonionic water-soluble cellulose ether that effectively serves for its function. As a result, the amount of cellulose ether added must be increased. The upper limit of average particle size is usually up to 500 xcexcm, and especially up to 300 xcexcm. The water-soluble cellulose ether having a particle size in the above range is available by grinding the raw material, sifting and collecting a fraction under appropriate classification conditions.
The nonionic water-soluble cellulose ethers which can be used herein include alkyl celluloses, hydroxyalkyl celluloses, and hydroxyalkyl alkyl celluloses. Illustrative examples include, but are not limited to, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxyethyl ethyl cellulose and hydroxypropyl methyl cellulose.
Preferably, the nonionic water-soluble cellulose ether has an (aerated) bulk density of 0.2 to 0.65 g/cm3.
Further, the nonionic water-soluble cellulose ether has a viscosity of 1,000 to 50,000 mPaxc2x7s, preferably 1,500 to 50,000 mPaxc2x7s, more preferably 3,000 to 50,000 mPaxc2x7s, as measured in a 1 wt % aqueous solution at 20xc2x0 C. by a Brookfield viscometer at 12 rpm.
On use, the admixture of the invention comprising the nonionic water-soluble cellulose ether, especially consisting of the nonionic water-soluble cellulose ether alone or as a mixture of two or more is added to an extrudable hydraulic composition. The amount of the admixture added (the total amount of nonionic water-soluble cellulose ethers) is an amount necessary to permit the hydraulic composition to be extruded, usually 0.1 to 2.0% by weight based on the entire components of the extrudable hydraulic composition excluding water, preferably 0.2 to 2.0% by weight and more preferably 0.2 to 1.5% by weight.
If necessary, another water-soluble polymer may be used along with the admixture of the invention for extrudable hydraulic compositions. Examples of other water-soluble polymers include partially saponified polyvinyl alcohol, modified starch, polyethylene oxide, wellan gum, and polyacrylamide.
The extrudable hydraulic composition of the invention contains the admixture defined above as well as conventional components such as hydraulic substances, aggregates, lightweight aggregates, and reinforcing fibers.
The hydraulic substances that harden in the presence of water include cement and gypsum. Cements include ordinary Portland cement, early-strength cement, blast furnace slag cement, fly-ash cement and alumina cement. Gypsum-based hydraulic substances include primarily the dehydrate, hemihydrate and anhydride forms of gypsum. The content of cement or gypsum-based hydraulic substances is not critical and may be set as needed to achieve the required strength.
Powdered silica and fly ash are typical aggregates. Besides, lightweight aggregates are used when weight reduction is desired, and include perlite, hollow microspheres, and styrene beads. Whether the aggregate is ordinary or lightweight, it is combined with the hydraulic substance so that the desired properties are achievable. The hydraulic substance and the aggregate are used in a weight ratio of from 10:90 to 100:0.
Reinforcing fibers are also useful in the hydraulic compositions. At present, pulp fibers that eliminate a concern about carcinogenicity become a substitute for asbestos and are widely used. In the practice of the invention, pulp fibers are advantageously used. Pulp fibers include fibers of virgin pulp, recycled paper pulp, and pulps originating from conifer and broadleaf woods, having an average length of about 200 to 2,000 xcexcm. Polypropylene, vinylon and acrylic fibers are also useful. From the fire resistance and other standpoints, fibers are preferably used in amounts of 1 to 10 parts by weight provided that the total of the entire components of the hydraulic composition excluding water is 100 parts by weight.
If necessary, setting accelerators and retarders, and surface active agents such as water-reducing agents and dispersing agents are used. These agents are effective for managing the physical properties of a fresh hydraulic composition immediately after mixing of components with water. Any agent meeting a particular purpose may be added in a conventional amount.
To the hydraulic composition of the invention, water is added. The amount of water is conventional though it is determined in accordance with the type of hydraulic composition or the like. Water is preferably used in amounts of 20 to 80 parts by weight provided that the total of the entire components of the hydraulic composition excluding water is 100 parts by weight.
The hydraulic composition of the invention is obtainable by mixing the aforementioned components in a conventional manner. The hydraulic composition thus obtained is formed and hardened into a hardened body by an extrusion molding or suitable method.